JP5923338B2 - Transistor element - Google Patents

Description

  The present invention particularly relates to a transistor element exhibiting excellent current modulation, and more particularly to a transistor element excellent in driving an organic EL display and the like and excellent in on / off ratio for large current modulation at a low voltage.

  In recent years, flat TVs and notebook computers have been widely used, and the required performance for display displays such as liquid crystal displays, organic EL displays, and electronic papers is also increasing. Furthermore, with the spread of high-function mobile phones and tablet terminals, display displays are becoming finer, smaller, and thinner. A field effect transistor (FET) is used for driving such display elements. Currently, FETs using silicon, which is an inorganic material, are used, but displays using organic transistor elements have been reported for the purpose of cost reduction, large area, and flexibility. Is expected.

  However, many of them are a combination of an organic field effect transistor (OFET) and a liquid crystal display unit or an electrophoresis cell. OFETs are difficult to obtain a large current due to their structure and low mobility, and few examples have been reported for use in driving elements of organic EL displays, which are current-driven devices that require large currents. Therefore, it is desired to develop an organic transistor element that can drive an organic EL display and operates with a large current at a low voltage.

  Currently, in order to obtain a large current using an OFET, it is necessary to shorten the channel length of the transistor element. However, the patterning technology with a view to mass production is to reduce the channel length to several μm or less. difficult. In order to solve this problem, a “vertical transistor structure” that can operate at a low voltage and a large current by flowing a current in the film thickness direction has been studied. In general, the thickness of an element used in a vertical sandwich device is several tens to several hundreds of nanometers, and it is possible to control the film thickness on the order of nm or less with high accuracy. The vertical transistor can easily realize a short channel length of 1 μm or less by setting the channel in the film thickness direction (vertical direction), and a large current may be obtained. So far, such vertical organic transistor elements have been depleted with polymer grid triode vertical transistors using a self-organized network structure of polyaniline film as grit electrodes, and fine striped intermediate electrodes. A static induction transistor (SIT) that controls the current between the source and the drain by modulating the layer width is known.

  In addition, a vertical organic transistor element that exhibits high-performance transistor characteristics by producing a laminated structure of organic semiconductor / metal / organic semiconductor has been proposed (Patent Document 1). In this vertical transistor element, an organic semiconductor layer and a striped intermediate metal electrode are provided between an emitter electrode and a collector electrode. In this organic transistor element, electrons injected from the emitter electrode are transmitted through the intermediate metal electrode, whereby current modulation similar to that of a bipolar transistor is observed, and the intermediate metal electrode acts like a base electrode. It is called an organic transistor (Metal-Base Organic Transistor: hereinafter referred to as MBOT).

  In MBOT, when an output voltage is applied to the emitter electrode and the collector electrode and no voltage is applied between the emitter electrode and the base electrode, almost no current flows. However, when a voltage is applied between the emitter electrode and the base electrode, the emitter electrode-collector A current flows between the electrodes. The current flowing between the emitter electrode and the collector electrode is the collector current, and the current flowing between the base electrode and the collector electrode is the base current. MBOT is an element capable of modulating the collector current by the base voltage because the collector current increases abruptly as compared with the base current that increases by the application of the base voltage. The “leakage current” that flows when voltage is applied between the emitter electrode and the collector electrode and no voltage is applied between the emitter electrode and the base electrode is OFF current, and the voltage is applied between the emitter electrode and the base electrode. The current that sometimes flows is the ON current. MBOT is a transistor element in which an OFF current is close to zero and a large ON current can be obtained.

  In addition, as a structure of an organic transistor (MBOT), MBOT has been reported that can be easily formed by stacking an organic semiconductor / metal / organic semiconductor by vacuum deposition on a transparent ITO electrode as a collector electrode (patent) Reference 2). As the organic semiconductor, dimethylperylenetetracarboxylic acid diimide (Me-PTCDI) and fullerene (C60), which are n-type organic semiconductor materials, are used. As the electrode material, Al is used as the base electrode, and Ag is used as the emitter electrode. It has been. This MBOT becomes a transistor element capable of large current modulation with an improved on / off ratio (ratio between ON current and OFF current) by introducing a dark current suppressing layer and heat-treating the base electrode. Thus, although MBOT is a vertical transistor, it does not require fine patterning of fine grid electrodes and stripe electrodes.

  Further, as an organic transistor element (MBOT), an organic semiconductor layer and a sheet-like base electrode are provided between an emitter electrode and a collector electrode, and an energy barrier layer and a charge transmission promoting layer are provided between the base electrode and the collector electrode. MBOT (Patent Document 3) and MBOT (Patent Document 4) using an organic semiconductor layer made of perylenetetracarboxylic acid diimide having a long-chain alkyl group on the collector electrode side as a collector layer have been proposed, It has been reported that good current modulation characteristics and on / off ratios can be obtained without heat treatment. Furthermore, MBOT in which the organic semiconductor layer of the emitter electrode and the base electrode has a diode structure has been reported as a transistor element having good amplification (Patent Document 5).

  In addition, as a vertical transistor, an organic semiconductor layer and a sheet-like base electrode are provided between an emitter electrode and a collector electrode. , N′-diphenyl-N, N′-di (1-naphthyl) -1,1′-biphenyl-4,4′-diamine (NPB) / fullerene (C60) heterojunction organic semiconductor layer transmission A conductive metal substrate organic transistor has been reported as a bipolar transistor (Non-patent Document 1).

  In addition, as a vertical transistor, an organic semiconductor layer and a comb-shaped base electrode are provided between an L-shaped emitter electrode and a collector electrode, and the organic semiconductor layer is BTQBT [Bis (1,2,5-thiadiazolo). -P-quinobis (1,3-dithiol)] is reported to exhibit a large current value and ON / OFF ratio despite being a hole transport material (Patent Document 6). .

In addition, there is a proposal for an organic transistor element (MBOT) using an organic semiconductor layer having high crystallinity between an emitter electrode and a collector electrode (Patent Document 7), which has a thickness comparable to that of a base electrode. As a transistor element using an organic semiconductor layer having a crystal size of MBOT, MBOT using methylperylene as an electron transporting material has a high current value of 300 mA / cm ² at a low voltage between the emitter and the collector and a large current value. It is described that an ON / OFF ratio of 200 is indicated.

JP 2003-101104 A JP 2007-258308 A JP 2009-272442 A JP 2010-263144 A International Publication No. 2011/027915 Pamphlet JP 2010-251472 A JP 2010-135809 A

J. et al. Hung et al, Organic Electronics, 10, 210 (2009)

  However, polymer grid triode type vertical transistors and electrostatic induction transistors (SIT) are difficult to achieve high performance and mass production due to the difficulty of forming an intermediate electrode. In addition, the organic transistor element (MBOT) described in Patent Documents 1 and 2 may have a high off-state current depending on the film thickness and structure, and the transistor has an organic semiconductor / metal / organic semiconductor stacked structure. Once manufactured, current modulation is not necessarily observed. Therefore, in order to exhibit stable performance, obtain a large current value, a high amplification factor, and a high on / off ratio, it is necessary to provide an oxide layer on the surface of the base electrode by heat treatment to form an off current suppression layer . In addition, the organic transistor element (MBOT) described in the above-mentioned Patent Document 3 amplifies the current without heating the electrode by providing an insulating current transmission promoting layer under the base electrode. However, it is difficult to obtain a large current value, a large amplification factor, and a large on / off ratio sufficient to operate an electronic device, and stable operation as an MBOT with a hole transporting material is difficult. is there.

  Moreover, in the organic transistor element described in Patent Document 6, current modulation is shown by forming an organic semiconductor layer with BTQBT as a hole transport material, but the materials that can be used are limited, and the synthesis of the materials is also possible. It is multi-stage and it is difficult to synthesize a large amount, and since the electrode shape of the element is comb-shaped or L-shaped and complicated, it is difficult to mass-produce stable elements by a simple manufacturing process.

  Further, in the organic transistor element described in Patent Document 7, a large current can be achieved by using an organic semiconductor layer having high crystallinity, but the ON / OFF ratio is ON when a dark current suppression layer is used. The / OFF ratio is about 250, and it is still difficult to drive the electronic device. Further, although there is a description of the hole transport material, there is no description as a specific example.

  Non-Patent Document 1 shows a current modulation action as a bipolar transistor element, and thus may be used for a complementary logic circuit or the like, but has a large current value and current sufficient to operate an electronic device. It is difficult to obtain enhancement of the above, and it is difficult to use it as a driving element such as an organic EL.

  Accordingly, an object of the present invention is to solve the above-described problems, and in particular, has a structure that can be stably provided by a simple manufacturing process and can also be mass-produced. An object of the present invention is to provide a transistor element (MBOT) having a large current modulation action and an excellent on / off ratio under a low voltage between an emitter electrode and a collector electrode.

  The above object is achieved by the present invention described below. That is, the present invention relates to a transistor having a laminated structure in which a sheet-like base electrode is disposed between an emitter electrode and a collector electrode, and p-type organic semiconductor layers are provided on the front and back sides of the base electrode. In the device, an organic semiconductor layer including at least one p-type organic semiconductor is provided between the emitter electrode and the base electrode, and the same or different p-type semiconductor material is formed between the base electrode and the collector electrode. Provided is a transistor element comprising a collector layer having a stacked structure of at least two p-type organic semiconductor layers each having a different HOMO level (maximum occupied orbital energy level) To do.

The following are mentioned as a preferable form of this invention. The collector layer comprises two organic semiconductor layers, a collector electrode side collector layer and a base electrode side collector layer, and the collector electrode side collector layer has a HOMO level (maximum occupied orbit energy level) of 4.5 to 5. The base electrode side collector layer is made of a p-type organic semiconductor layer at a HOMO level (maximum occupied orbital energy level) of 5.0 to 6.0 eV, and the collector is made of a p-type organic semiconductor layer at 5 eV. The base electrode side collector layer has a higher HOMO level (highest occupied orbit energy level) than the electrode side collector layer. The surface roughness of the p-type organic semiconductor layer is 5 nm or less in terms of mean square roughness (RMS). The organic semiconductor layer disposed on the base electrode side among the plurality of p-type organic semiconductor layers forming the collector layer contains diindenoperylene, dinaphthothienothiophene, nickel phthalocyanine, and derivatives thereof. To become a. Of the p-type organic semiconductor layers forming the collector layer, the organic semiconductor layer disposed on the collector electrode side contains phthalocyanine, diindenoperylene and derivatives thereof. The p-type organic semiconductor layer disposed between the emitter electrode and the base electrode contains pentacene, phthalocyanine, and derivatives thereof. A current transmission facilitating layer is further provided in a state of being laminated on one or both of the front and back surfaces of the sheet-like base electrode. The current transmission promoting layer is made of lithium fluoride. The film pressure of the current transmission promoting layer is from 0.1 nm to 100 nm. A collector current I _C-ON that flows by applying a voltage (V _B ) between the emitter electrode and the base electrode, and further applying a voltage (V _C ) between the emitter electrode and the collector electrode; ON / OFF, which is the ratio of the collector current I _C-OFF that flows when the voltage (V _C ) is applied between the emitter electrode and the collector electrode without applying the voltage (V _B ) between the base electrode and the base electrode (I _C-ON / I _C-OFF ) is a current modulation property of 1,000 or more.

  According to the present invention, an organic transistor element (MBOT) having the following excellent characteristics is provided. The transistor element of the present invention has a laminated structure in which a sheet-like base electrode is disposed between an emitter electrode and a collector electrode, and a p-type organic semiconductor layer is provided on each of the front and back sides of the base electrode. One feature is that an organic semiconductor layer containing at least one p-type organic semiconductor is provided between the emitter electrode and the base electrode, and a HOMO level and a collector electrode are provided between the base electrode and the collector electrode. It is further characterized in that a collector layer having a layer structure of at least two layers each comprising a different p-type organic semiconductor layer is provided. In the transistor element of the present invention, a plurality of p-type organic semiconductor layers are arranged as described above with respect to the base electrode, and more than two p-layers having the above-mentioned specific relationship between the base electrode and the collector electrode. By providing the type organic semiconductor layer, it is possible to stably obtain a current modulation action that enables a large current at a low voltage.

  The organic transistor element (MBOT) of the present invention has high performance described later, and drives organic EL and electronic paper driven by large current modulation, particularly as various display driving elements and organic light emitting transistor elements. It is useful as an element. The transistor elements that drive them require contrast between on and off, and are required to have a larger on / off ratio and suppression of dark current. When the on / off ratio is low and the dark current is large, there arises a problem that the organic EL emits light even when it is off. On the other hand, the transistor element of the present invention has high performance as a driving transistor element because it has a high on / off ratio and excellent large current modulation characteristics and frequency characteristics in a low voltage region, and is sufficiently applied. Is possible.

  Further, the organic transistor element of the present invention is capable of large current modulation in a low voltage region, can reduce the area occupied by the transistor element in one pixel, and can improve the aperture ratio in the display. By applying this, it is possible to achieve a high-performance and high-efficiency display. It can also be created by vapor deposition, and transistor elements can be formed on flexible substrates such as plastics, making it possible to create smaller and lighter, lighter, thinner displays and devices. .

More specifically, the transistor element provided by the present invention applies a voltage (V _C ) between the emitter electrode 12 and the collector electrode 11 as shown in FIG. A current modulation type transistor element in which a collector current I _{C that} is modulated as compared with a base current I _B that flows between the emitter electrode 12 and the base electrode 13 flows when a voltage (V _B ) is applied between the transistor 12 and the base electrode 13. Become. More specifically, the current amplification factor (collector current I _C / base current I _B ) of the modulated collector current I _C reaches 1,000 or more, further 10,000 or more. The organic transistor element provided in the present invention applies a voltage (V _B ) between the emitter electrode 12 and the base electrode 13 and further applies a voltage (V _C ) between the emitter electrode 12 and the collector electrode 11. A voltage (V _C ) is applied between the emitter electrode 12 and the collector electrode 11 without applying the flowing collector current I _C-ON (hereinafter referred to as ON current or on-current) and the voltage (V _B ). ON / OFF (I _C-ON / I _C-OFF ) (hereinafter referred to as ON / OFF ratio or ON / OFF) which is a ratio to collector current I _C-OFF (hereinafter referred to as OFF current or OFF current). (Denoted as a ratio) shows an extremely excellent current modulation property of 1,000 or more, or even 10,000 or more, and is expected to be applied to various applications.

3A and 3B each illustrate a structure of a transistor element of the present invention. 4A and 4B illustrate a structure of a transistor element according to an embodiment of the present invention. 8A and 8B illustrate a structure of a transistor element of a comparative example. 4A and 4B illustrate output characteristics (I _C −V _B curve) of a transistor element of the present invention. 4A and 4B illustrate output characteristics (I _B -V _B curve) of a transistor element of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be carried out without departing from the gist of the present invention.

  First, according to the present invention, an organic semiconductor layer and a sheet-like base electrode are provided between an emitter electrode and a collector electrode, and a p-type organic semiconductor layer is disposed on each of the front and back sides of the base electrode. The organic transistor element (MBOT) will be described. In the organic transistor element (MBOT) of the present invention, an organic semiconductor layer including at least one p-type organic semiconductor is provided between the emitter electrode and the base electrode, and the base electrode and the collector electrode are provided. A collector layer having at least two layers of p-type organic semiconductor layers each having a different HOMO level and / or semiconductor material is provided. In the present invention, the organic semiconductor layer disposed between the emitter electrode and the collector electrode with the base electrode interposed therebetween is called the collector electrode side, and the emitter electrode side is called the emitter layer. The collector layer is composed of at least two different p-type organic semiconductor layers. In the present invention, for example, when the collector layer is formed of two layers made of two different types of chemical structures, one of them is called a collector electrode side collector layer and the other is called a base electrode side collector layer. .

  One example of the structure of the transistor element (MBOT) of the present invention is shown in FIG. 1. As shown in FIG. 1, the element of the present invention is a simple stacking process having a stacked structure of organic semiconductor / electrode / organic semiconductor. It is a vertical organic transistor that can be manufactured by As shown in FIG. 1, the structure is such that a base electrode 13 and an organic semiconductor layer having the following specific configuration are sandwiched between a collector electrode 11 and an emitter electrode 12 formed on a substrate 10. . The organic semiconductor layer is configured by a collector layer 22 (a base electrode side collector layer 22A and a collector electrode side collector layer 22B) made of a p-type organic semiconductor disposed between the collector electrode 11 and the base electrode 13, and an emitter electrode 12 And an emitter layer 21 including a p-type organic semiconductor disposed between the base electrode 13 and the base electrode 13 sandwiched between these organic semiconductor layers. That is, the transistor element of the present invention illustrated in FIG. 1 includes a collector electrode 11, an emitter electrode side collector layer 22B, a base electrode side collector layer 22A, a base electrode 13, an emitter layer 21, and an emitter electrode 12 in this order on a substrate 10. It has a laminated structure.

  One of the features of the transistor element of the present invention is that the structure of the collector layer 22 made of different p-type organic semiconductors has a collector layer 22B formed on the collector electrode side and a collector layer 22A formed on the base electrode portion side. It is to make a laminated structure. As a result of intensive studies, the present inventors have achieved the following remarkable effects by adopting the unique structure described above, and can achieve a useful organic transistor element (MBOT) expected to be put to practical use. I found. That is, in the collector layer 22, for example, the effect of forming a stacked structure of p-type organic semiconductor layers formed of two kinds of p-type organic semiconductor materials having different HOMO levels, charges (holes) are emitted from the emitter layer. 21 can be efficiently injected into the collector layer 22A, and the charge sent from the collector layer 22A to the collector layer 22B can move to the collector electrode 11. Therefore, the collector layer 22 having the above-described stacked structure can control the flow of current, increase the collector current flowing from the emitter electrode 12 to the collector electrode 11, suppress the leakage current, and reduce the off current. It has the effect of maintaining a small size, and can stably perform a large output modulation operation and a current modulation operation even in a low voltage region, and is useful for an organic transistor element (MBOT).

  Furthermore, the present inventors have obtained new findings on the following points, and have found that this is effective in the practical application of organic transistor elements (MBOT). In the base electrode formed on the collector layer, which is a characteristic of the transistor element (MBOT) of the present invention, the roughness of the base electrode is determined by the surface roughness of the collector layer. In a conventional organic transistor (MBOT), it is common to form irregularities on the base electrode, and it has not been done so far to make the collector layer a smooth surface. On the other hand, the present inventors can make the film thickness of the base electrode uniform by smoothing the collector layer, and this is effective for transferring charges (holes) from the emitter layer 21 to the collector layer 22A. This has the effect of increasing the collector current flowing from the emitter electrode to the collector electrode, suppressing the leakage current, and keeping the off current small. It has been found that the current modulation operation can be stabilized and is useful for an organic transistor element (MBOT).

  Hereinafter, the performance of the transistor element of the present invention will be described more specifically. The transistor element of the present invention has a large current value, current amplification factor, and ON / OFF ratio which is a ratio of current at ON and OFF, and is formed, for example, by a laminated structure composed of copper phthalocyanine and diindenoperylene. When the performance of the transistor element of the present invention having the collector layer formed is compared with the performance of the transistor element having a collector layer having a single-layer structure formed of diindenoperylene, the collector current is about 1,600 times larger. Thus, the current amplification factor was 1,200 times or more, and the ON / OFF ratio was about 140 times, confirming that excellent performance was exhibited. The present inventors consider the principle that the above-described remarkable performance is obtained by the transistor element of the present invention as follows. That is, as the mechanism, [1] the collector current value is greatly increased although the base current value is hardly changed, [2] the OFF current is hardly increased, [3] the collector When the ratio of the film thickness of 22A and 22B constituting the layer is changed, the current value changes, so that when the charge (holes) accelerated by the voltage passes through the base electrode from the emitter layer and flows into the collector layer, the base electrode In addition to improving the current transmission rate in the emitter layer, it is possible to efficiently inject the holes injected into the emitter layer from the emitter electrode into the collector layer, and charge (holes) can be injected into the collector layer. It is possible to control the flow from the base electrode to the collector electrode side, and a mechanism that greatly improves the charge transport property can be considered.

  Further, as described below, the transistor element of the present invention is more excellent in performance because a large ON current can be obtained by using an organic semiconductor layer having high surface smoothness as a collector layer. More specifically, in the transistor element of the present invention, the surface roughness of the collector layer is made smooth so that the mean square roughness (RMS) is 5 nm or less, thereby further improving the performance. It was confirmed that an effect was obtained. For example, the transistor element of the present invention having a collector layer formed of a laminated structure made of copper phthalocyanine and diindenoperylene (RMS = 1.68 nm), copper phthalocyanine and dinaphthothienothiophene (RMS = 13.6 nm) Comparing the performance with the transistor element of the present invention having a collector layer formed by a laminated structure made of the element, the collector current of the element made of copper phthalocyanine and diindenoperylene is about 4.5 times larger, and the current amplification The rate was 6.4 times or more, and the ON / OFF ratio was about 3.3 times, indicating superior performance. The present inventors consider the principle of obtaining the above remarkable performance as follows. That is, as a mechanism, when comparing the two, [1] the collector current value has greatly increased despite the fact that the base current value has hardly changed, and [2] the OFF current has hardly increased. [3] Diindenoperylene (HOMO = 5.47 eV: measured value) and dinaphthothienothiophene (HOMO = 5.49 eV: measured value) have almost the same HOMO, so that the charge accelerated by the base voltage When (holes) pass through the base electrode from the emitter layer and flow into the collector layer, it is considered that the local electrode is not applied because of the smoothness of the base electrode, and the current transmittance is improved.

Here, when a collector voltage Vc is applied between the emitter electrode and the collector electrode and a base voltage V _B is applied between the emitter electrode and the base electrode, the current flowing in the transistor element of the present invention is the base voltage. As a result, holes injected from the emitter electrode are accelerated, pass through the base electrode, and reach the collector electrode. That is, the base current I _B that flows when the base voltage V _B is applied between the emitter electrode and the base electrode is considered to be a current that does not pass through the base electrode, and the collector current that flows between the emitter electrode and the collector electrode when the base voltage is applied. Amplified to Ic. Therefore, the transistor element of the present invention having the above-described performance can stably obtain a current modulation action similar to that of a bipolar transistor, and enables large output modulation and current amplification.

Further, when the on-current flowing through the transistor element of the present invention is rectified by the layer structure of the collector layer, holes injected from the emitter electrode are accelerated and transmitted through the base electrode by the action of the base voltage, and the collector Reach the electrode. That is, the base current I _B that flows when the base voltage V _B is applied between the emitter electrode and the base electrode is considered to be a current that does not pass through the base electrode, and the collector current that flows between the emitter electrode and the collector electrode when the base voltage is applied. a form that is amplified to I _C. Therefore, the transistor element of the present invention having the above-described performance can stably obtain a current modulation action similar to that of a bipolar transistor, and enables large output modulation and current amplification.

On the other hand, the off-state current of the transistor element (MBOT) of the present invention shows a rectifying effect due to the gradient of the HOMO level of the organic semiconductor material forming the collector layer. Not flowing. When the voltage V _B is not applied (V _B = 0V), it is possible to effectively suppress leakage current (off current flowing when OFF) unnecessary for transistor operation between the base electrode and the collector electrode. As a result, the on / off ratio can be improved. Therefore, when an organic transistor element (MBOT) is used as a driving transistor element for an organic EL, if the dark current is large, the organic EL element emits light when it is OFF, and the contrast when ON and OFF is reduced. The off ratio is desirably 500 or more, preferably 1,000 or more, more preferably 10,000 or more on / off ratio is required for the driving transistor element. According to the transistor element of the present invention, It can be 10,000 or more and can be easily achieved.

Furthermore, the current value of the transistor element (MBOT) of the present invention can be greatly amplified even in the low voltage region, and a large current can be obtained, which is extremely useful from this point. In general, the organic EL element is an element that is driven in a low voltage region, and the driving transistor element is required to output a large current at several volts. Organic EL elements can achieve high intensity light emission by increasing the applied voltage, but they can realize high intensity light emission, but they cause deterioration and decomposition of the light emitting element material, shorten the life of the element, and provide stable light emission for a long time. Can not. Therefore, the drive voltage is about 1 to 20V, preferably 5V or less. At this time, the current density value modulated by the transistor element in the low voltage region is not particularly limited, but is preferably 1 mA / cm ² to 500 mA / cm ² , more preferably 1 mA / cm ² to 200 mA. / Cm ² is preferable. When used as a light emitting element, if the current density value is 1 mA / cm ² or less, sufficient light emission cannot be achieved, and sufficient light emission intensity cannot be obtained. In addition, a device having a current density value exceeding 500 mA / cm ² cannot obtain a sufficient on / off ratio, and has a problem that a dark current is generated and light is emitted from the light emitting device even when it is OFF (voltage 0 V). May occur.

  Since the collector layer of the transistor element of the present invention has a laminated structure composed of at least two p-type organic semiconductors, there is also an advantage of manufacturing conditions that a wide range of p-type organic semiconductor materials can be applied. . That is, in the present invention, the material for forming the collector layer may be any material that can efficiently transport holes, and any material that can form the p-type organic semiconductor layer can be used without any problem. That is, in the present invention, the organic semiconductor material used for forming the p-type organic semiconductor layer may be any material that transports holes (hole transporting material). Any collector layer in which p-type organic semiconductor layers having different levels are laminated can be used without particular limitation.

  The organic semiconductor film constituting the transistor element of the present invention desirably has an appropriate energy level. Therefore, as a preferred configuration of the present invention, in the p-type organic semiconductor layer (collector layer) provided between the base electrode and the collector electrode, the collector electrode side collector layer has a HOMO level (maximum occupied orbital energy). P) a p-type organic semiconductor layer at 4.5 to 5.5 eV with a base electrode side collector layer at a HOMO level (maximum occupied orbital energy level) of 5.0 to 6.0 eV For example, the HOMO level (maximum occupied orbital energy level) of the base electrode side collector layer is higher than that of the collector electrode side collector layer. Further, the HOMO level (the highest occupied molecular orbital energy level) of the organic semiconductor material forming the emitter layer is not particularly limited, but according to the study by the present inventors, the HOMO level of the emitter layer is 4. The base electrode side collector layer is formed of an organic semiconductor material having a HOMO level (maximum occupied molecular orbital energy level) of 5.3 to 6.0 eV. In this case, due to the difference in the HOMO level, holes injected from the emitter layer can move to the collector electrode more efficiently, and as a result, a larger current can be obtained.

  The base electrode side collector layer constituting the transistor element of the present invention is one in which holes are efficiently injected from the emitter layer. As a p-type organic semiconductor material forming the layer, for example, diindenoperylene (DIP), dinaphthothienothiophene (DNTT), metal phthalocyanine, metal-free phthalocyanine. Among these, indenoperylene, which can form a smooth base electrode on the collector layer surface, is particularly preferable. The HOMO energy level measured with an atmospheric photoelectron spectrometer (AC-3, manufactured by Riken Keiki Co., Ltd., the following is also measured) of these materials, and the surface mean square roughness (RMS) measured by AFM are: These are 5.49 eV and 13.6 nm for DNTT, 5.49 eV and 1.68 nm for DIP, and 5.23 eV and 8.36 nm for Ni phthalocyanine, respectively. Therefore, when any of these materials is used, holes injected efficiently from the emitter layer can be efficiently moved to the collector electrode side collector layer described later, and a large current can be obtained. According to the study by the present inventors, among these, particularly when DIP is used on the collector layer surface, a larger current value can be obtained.

  The collector layer formed on the collector electrode side constituting the transistor element of the present invention differs from the collector layer formed on the base electrode side described above in the HOMO level. Holes are often injected. Examples of the p-type organic semiconductor material for forming the collector electrode side collector layer include metal-free phthalocyanine and metal phthalocyanine. For example, the HOMO energy level of copper phthalocyanine measured by an atmospheric photoelectron spectrometer is 5.15 eV, which controls the flow of charge that sends charge from the collector layer formed on the base electrode side to the collector electrode. It becomes possible.

  The emitter layer constituting the transistor element of the present invention is an organic semiconductor thin film formed of a p-type organic semiconductor. The material for forming the emitter layer may be any material that can efficiently transport holes, and any material that can form the p-type organic semiconductor layer can be used without any problem. The organic semiconductor material used for forming the p-type organic semiconductor layer functions as a hole transport semiconductor, and the material used is not particularly limited as long as it is a material that transports holes (hole transport material). Can be used.

  The emitter layer constituting the transistor element of the present invention preferably has an appropriate energy level. In the emitter layer, holes injected from the emitter electrode move to the base electrode interface, pass through the base electrode, and are injected into the collector layer. As a material for the formation, injection of holes from the base electrode is efficient. A HOMO level (highest occupied molecular orbital energy level) that is often performed and easily injects holes into the collector layer is preferable. Specifically, an organic semiconductor material having a HOMO level of 4.5 to 5.5 eV is preferable, and an emitter layer made of such a material can efficiently transfer injected holes to the collector electrode. , A larger current can be obtained. In the emitter layer, holes injected from the emitter electrode move to the base electrode interface, pass through the base electrode, and are injected into the collector layer. As a specific forming material, holes are injected from the base electrode. Can be efficiently performed and holes can be easily injected into the collect layer. For example, a compound selected from pentacene, metal-free phthalocyanine, metal phthalocyanine, dinaphthothienothiophene, and diindenoperylene, and derivatives thereof can be used.

  The material for forming the base electrode side collector layer constituting the transistor element of the present invention may be any material that can be efficiently injected from the emitter layer. As described above, as a particularly suitable material, for example, Noperylene (DIP) and dinaphthothienothiophene (DNTT) are mentioned. According to the study by the present inventors, these materials have a measured value of the HOMO level that has an energy suitable for efficiently transferring holes injected from the emitter layer to the collector layer on the collector electrode side. It has a level. Here, the HOMO energy levels of the above materials measured by an atmospheric photoelectron spectrometer are 5.47 eV (DIP) and 5.49 eV (DNTT), respectively. As a more preferable configuration of the transistor element of the present invention, an organic semiconductor layer (collector layer) on the base electrode side is formed of the above-described material, and the emitter layer between the emitter electrode and the base electrode is formed as a HOMO level. The base electrode and the organic semiconductor layer (collector layer) on the collector electrode side are formed by using a suitable organic semiconductor material having a maximum occupied orbit energy level of 4.5 to 5.5 eV. Examples thereof include those formed of a material whose level (maximum occupied orbital energy level) is in the range of 5.3 to 6.0 eV. In the case of the above configuration, holes injected from the emitter layer can efficiently move to the collector electrode due to the difference in HOMO levels of the respective forming materials, and a larger current can be obtained.

(Current transmission enhancement layer)
In a preferred embodiment of the transistor element of the present invention, a current transmission facilitating layer is further formed in a laminated state on one or both of the front and back surfaces of the sheet-like base electrode. More specifically, the current transmission facilitating layer is required at one or both of the positions between the base electrode and the collector layer (collector layer side) and between the base electrode and the emitter layer (emitter layer side). It is preferable that these current transmission promotion layers have a structure laminated on the base electrode. According to the study by the present inventors, the collector layer side current transmission promoting layer formed between the base electrode and the collector layer is (1) to reduce the OFF current, and (2) the ratio of the base current to the collector current is The effect of increasing the gain and increasing the gain is exhibited. The emitter layer side current transmission promoting layer formed between the base electrode and the emitter layer (1) increases the collector current by increasing the efficiency of charge transfer to the collector layer and improving the charge injection rate. 2) The OFF current can be reduced by improving the electrode interface. As a result, the current amplification factor and the ON / OFF ratio are further increased. Furthermore, in the low voltage region, large output modulation and large current modulation have the effect of being able to operate stably.

  As described above, the current transmission promotion layer that can constitute the transistor element of the present invention is formed so that the current transmission promotion layer and the base electrode have a laminated structure. As a material for forming the current transmission promoting layer, any material can be used without any problem as long as it is a material that improves the current transmittance in which the current passing through the base electrode increases. Specifically, as a material for forming the current transmission facilitating layer, a material known so far as an electron injection layer can be used. For example, an alkali metal compound can be preferably used. And lithium fluoride.

According to the study by the present inventors, the function brought about by forming the current transmission facilitating layer as necessary in the transistor element of the present invention is as described below. For example, when an aluminum electrode is used as a base electrode and sandwiched between layers made of lithium fluoride, which is a current transmission promoting material, to form a base electrode portion, a collector layer and an emitter layer are formed on each side of the base electrode on both sides. The current amplification factor of the MBOT formed in the above is more than 77 times that of the MBOT in which the lithium fluoride layer is formed only on one side of the base electrode, and the current I _C does not have the lithium fluoride layer. It was confirmed that a large current could be obtained by doubling. The principle for obtaining the above effect is as follows: [1] the current gain is greatly improved, [2] the OFF current is not increased, and [3] the current value is decreased when the current transmission promoting layer is thickened. Therefore, the presence of the current transmission facilitating layer suppresses diffusion of the material forming the base electrode into the semiconductor layer, and holes accelerated by the voltage flow from the emitter layer to the collector layer. In some cases, a mechanism for improving the current transmittance in the base electrode portion is also conceivable.

  Furthermore, the transistor element of the present invention can eliminate the need for fine patterning of the base electrode as in the conventional SIT structure, can perform large current modulation at a low voltage, and has a high on / off ratio. An element can be obtained. In addition, the transistor element of the present invention can be manufactured only by a vapor deposition method. Therefore, it is possible to form an element on a flexible substrate such as plastic, which is simple and reduced in size and weight. A practical light-emitting transistor element having a structure can be easily manufactured. The transistor element of the present invention can have a light emitting element part including a light emitting layer whose collector layer is an organic EL, and the light emitting element part includes a hole injection layer, a hole transport layer, an electron A light-emitting transistor element having a light-emitting element part composed of one or more layers selected from a transport layer and an electron injection layer is obtained.

Next, each structure and material of the transistor element of the present invention will be described.
(substrate)
The organic transistor element of the present invention is usually used by being formed on a substrate as described below. The substrate used in this case may be any material that can maintain the shape of the transistor element. For example, inorganic materials such as glass, alumina, quartz, and silicon carbide, metal materials such as aluminum, copper, and gold, polyimide films, and polyester films A plastic substrate such as polyethylene film, polystyrene, polypropylene, polycarbonate, or polymethyl methacrylate can be used. When a plastic substrate is used, a flexible transistor element that is lightweight and excellent in impact resistance can be manufactured. In the case of bottom emission in which light is emitted from the substrate side when used as a light emitting transistor element in which an organic light emitting layer is formed, it is desirable to use a substrate having a high light transmittance such as a plastic film or glass. These substrates may be used alone or in combination. As for the size and shape of the substrate, any device such as a card shape, a film shape, a disk shape, or a chip shape can be used without any problem as long as a transistor element can be formed.

(Organic semiconductor layer)
As described above, the organic transistor element of the present invention is characterized in that the p-type organic semiconductor layer to be formed includes a collector layer 22 provided between the collector electrode and the base electrode, as shown in FIG. And the emitter layer 21 formed between the emitter electrodes, and the collector layer 22 among them has a laminated structure of two or more layers each consisting of different p-type organic semiconductor layers. In addition, the base electrode and the collector layer and the emitter layer, which are p-type organic semiconductor layers, are stacked directly or via a current transmission promoting layer (see FIGS. 1 and 2). Hereinafter, the p-type organic semiconductor layer will be described separately for the collector layer and the emitter layer.

<Emitter layer>
The emitter layer 21 constituting the organic transistor element of the present invention is made of a p-type organic semiconductor, and can be used without any problem as long as it is a material that transports holes. If necessary, a multilayer structure with another p-type organic semiconductor layer, a diode structure with an n-type organic semiconductor layer, or a stacked structure with a hole injection layer may be used.

  The p-type organic semiconductor layer essential for the emitter layer constituting the present invention receives holes from the emitter electrode and supplies them to the base electrode, and in some cases, a paired n-type organic semiconductor layer, or an interface thereof Has the function of transporting to the vicinity. As a material for forming the p-type organic semiconductor layer, any general p-type semiconductor material can be used without particular limitation. For example, pentacene, metal-free phthalocyanine, metal phthalocyanines (Cu-Pc, VO-Pc, Ni -Pc), naphthalocyanine, indico, thioindigo, anthracene, quinacridone, oxadiazole, triphenylamine, triazole, imidazole, imidazolone, pyrazoline, tetrahydroimidazole, polythiophene, porphyrin, dinaphthothiophene, etc., or derivatives thereof Can be used. In addition to the p-type organic semiconductor materials listed above, a hole transporting material that functions as a p-type organic semiconductor material can also be used for forming the emitter layer.

  The p-type semiconductor material forming the emitter layer constituting the organic transistor element of the present invention is electrically stable, has an appropriate ionization potential and electron affinity, and has a HOMO level of 4.5 to 5 An organic semiconductor material at .5 eV is preferable, more preferably 4.5 to 5.3 eV, and even more preferably smaller than the HOMO level of the base electrode side collector layer. Particularly preferred materials for the p-type semiconductor layer forming the emitter layer include pentacene, phthalocyanines such as copper phthalocyanine and metal-free phthalocyanine.

  However, as a material for forming the p-type semiconductor layer of the emitter layer, a material other than these may be used as long as it has a property of transporting more holes than electrons. In this case, the p-type semiconductor layer may have not only a single layer structure using a single component but also a mixed layer composed of two or more components and a laminated structure composed of two or more organic semiconductor layers. As a method for forming the p-type organic semiconductor layer, it can be formed by various printing methods and coating methods using a vapor deposition method or a solution or dispersion containing these compounds.

The p-type organic semiconductor layer forming the emitter layer constituting the organic transistor element of the present invention desirably has a high charge mobility, and preferably at least 0.0001 cm ² / V · s. The emitter layer 21 is preferably basically thinner than the collector layer, and the emitter layer has a thickness of 300 nm or less, preferably about 10 nm to 300 nm. When the thickness of the emitter layer is less than 10 nm, the diode structure may not be formed in part, and it is considered that the transistor performance is lowered or the problem of conduction occurs and the yield is lowered. Absent. On the other hand, if the thickness of the emitter layer exceeds 300 nm, there is a problem that the manufacturing cost and the material cost increase, which is not preferable.

<Collector layer>
The collector layer constituting the organic transistor element of the present invention is formed of a p-type organic semiconductor material so as to have a laminated structure including two or more p-type organic semiconductor layers between the base electrode and the collector electrode. And as a material which forms this collector layer, the p-type organic-semiconductor material normally used as an organic semiconductor is mentioned, All can be used. The p-type semiconductor material is not particularly limited as long as it is a material that transports holes, and a commonly used p-type organic semiconductor material can be used, and the p-type semiconductor used in the emitter layer described above. Any material can be used.

  The material for forming the collector layer constituting the organic transistor element of the present invention can be used without particular limitation as long as it is a p-type semiconductor material, but the laminated structure composed of two or more different p-type organic semiconductor layers is The following is preferred. That is, the base electrode side collector layer formed on the base electrode side is a p-type organic semiconductor layer made of a material having a HOMO level (maximum occupied orbital energy level) in the range of 5.0 to 6.0 eV. More preferably, among materials having a HOMO level in this range, diindenoperylene (HOMO: 5.47 eV), dinaphthothienothiophene (HOMO: 5.49 eV), and derivatives thereof It is preferable that it is a layer. In this case, the derivatives include alkyl groups such as methyl group, ethyl group, butyl group, 2-ethylhexyl group, octyl group, dodecyl group, octadecyl group, heteroalkyl group having a hetero group in the alkyl group, and amino group. , A compound having a functional group such as an amide group or a carboxyl group. According to the study by the present inventors, the p-type organic semiconductor material has these functional groups, thereby increasing the solubility in a solvent. As a result, the printing method is applied when forming the p-type organic semiconductor layer. In addition to being able to easily form a smooth semiconductor surface, there is a case where charge transferability may be improved by interaction with a functional group, which is more preferable. The p-type organic semiconductor thin film (layer) made of these materials can be formed using a single material, but may be a mixed layer formed of a mixed material composed of two or more components. Furthermore, the collector layer constituting the organic transistor element of the present invention may have a laminated structure composed of two or more different p-type organic semiconductor layers, and has a laminated structure in which other organic semiconductor layers are further laminated. May be.

Moreover, the film thickness of the collector layer which comprises the organic transistor element of this invention can mention normally 50 nm-5,000 nm, Preferably it is about 100 nm-500 nm. If the thickness is less than 50 nm, it is not preferable because it may not operate as a transistor element. On the other hand, if the thickness exceeds 5,000 nm, it is not preferable because the manufacturing cost and material cost increase.
However, the charge mobility of the collector layer is desirably high, and at least 0.0001 cm ² / V · s or more is desirable. If the charge mobility is low, there is a possibility that problems such as performance as a transistor element, for example, a small on-current may occur, which is not preferable.

(electrode)
The electrode used for the transistor element of the present invention will be described. As the electrodes constituting the transistor element of the present invention, there are a collector electrode 11, an emitter electrode 12, and a base electrode 13. As shown in FIG. 1, the collector electrode 11 is provided on the substrate 10, and the base electrode 13 is The p-type organic semiconductor layer is provided so as to be buried between the emitter layer 21 which is a p-type organic semiconductor layer and the collector layer 22 having a laminated structure, and the emitter electrode 12 is located at a position facing the collector electrode 11. 21 and 22 and the base electrode 13 are provided.

The materials used for each electrode constituting the transistor element of the present invention are preferably as follows. For example, since the collector layer 22 constituting the transistor element of the present invention is a p-type semiconductor layer made of a p-type organic semiconductor, examples of the material for forming the collector electrode 11 include ITO (indium tin oxide), indium oxide, Examples include transparent conductive films such as IZO (indium zinc oxide), SnO ₂ , and ZnO, metals such as gold, silver, and copper, conductive polymers such as polyaniline, polypyrrole, polyalkylthiophene derivatives, and polysilane derivatives. . On the other hand, the material for forming the emitter electrode 12 includes simple metals such as aluminum and silver, magnesium alloys such as Mg—Ag and Mg—In, aluminum alloys such as Al—Li, Al—Ca, and Al—Mg, Li, and Ca. And metals having a small work function such as an alloy of these alkali metals.

  In the present invention, the dark current at the time of OFF is suppressed, and the electrode is formed on aluminum as a base electrode that achieves a high on / off ratio, and then the surface of the electrode is oxidized by thermal oxidation treatment in air. It is also a preferable form to use a base electrode on which a film is formed. In addition, by using an electrode having a layer structure made of an aluminum layer / lithium fluoride layer as a base electrode, it is possible to form a transistor element having a high ON / OFF ratio with a large ON current and a suppressed dark current. It becomes.

  The thickness of the base electrode used in the transistor element of the present invention is preferably 0.5 nm to 100 nm, more preferably 1 nm to 30 nm, still more preferably 5 nm to 20 nm. If the thickness of the base electrode is 100 nm or less, the base electrode can easily transmit electrons accelerated by the base voltage Vb. Note that the base electrode can be used without any problem if it is provided in the semiconductor layer without a break (that is, without a defect such as a hole or a crack). Since it may not operate, it is not preferable.

  As a method for forming an electrode used in the transistor element of the present invention, a vacuum process such as vacuum deposition, sputtering, CVD, or a coating method may be used for the collector electrode and the emitter electrode among the above-mentioned electrodes. The thickness of the electrode formed by these methods varies depending on the material used, but is preferably about 10 nm to 1,000 nm, for example. If the thickness is less than 10 nm, it may not operate as a transistor element. If the thickness exceeds 1,000 nm, both the manufacturing cost and the material cost increase, which is not preferable.

(Dark current suppression layer)
The transistor element of the present invention may have a dark current suppressing layer formed as follows. As the method, it is preferable to form the base electrode by heat treatment after the base electrode is formed. Furthermore, in the transistor element of the present invention, the base electrode is made of metal, and an oxide film of the base electrode is formed on one or both surfaces of the base electrode, whereby the voltage V _B is generated between the emitter electrode and the base electrode. The dark current that flows when no voltage is applied can be effectively suppressed.

  In addition, the dark current is suppressed by an aluminum oxide film on the surface of the electrode by thermal oxidation in air after forming the electrode with aluminum as a base electrode that suppresses dark current during OFF and achieves a high on / off ratio. It is also preferable to use a base electrode in which a layer is formed. In addition, by using an electrode having a layer structure made of an aluminum layer / lithium fluoride layer as a base electrode, it is possible to form a transistor element having a high ON / OFF ratio with a large ON current and a suppressed dark current. It becomes.

  According to these aspects of the present invention, since the dark current suppression layer is provided between the collector electrode and the base electrode, it is possible to effectively suppress the flow of dark current. / Off ratio can be improved. The transistor element of the present invention thus configured apparently effectively functions as a current modulation type transistor element similar to a bipolar transistor, and is an excellent organic material exhibiting a high on / off ratio, a large collector current, and a current amplification factor. It functions as a transistor element.

  EXAMPLES Hereinafter, although an Example and comparative example of this invention are given and this invention is demonstrated in detail, this invention is not limited to this. The HOMO level of the organic semiconductor material is measured with the above-described atmospheric photoelectron spectrometer, and the average square roughness RMS is measured with an atomic force microscope for the surface roughness of each p-type organic semiconductor layer. The crystal particle diameter was calculated from the half-value width by X-ray diffraction and confirmed with an atomic force microscope.

The transistor elements fabricated in Examples and Comparative Examples were evaluated by the following method. First, the method will be described.
(Evaluation of transistor elements)
For the manufactured transistor element, an applied voltage (V _C ) is applied between the emitter electrode and the collector electrode, and a base voltage (V _B ) applied between the emitter electrode and the base electrode is set to 0V to −3, −5, −10V. Modulated with range. The output modulation characteristic is measured by applying a collector voltage (V _C ) between the emitter electrode and the collector electrode, and further applying a base voltage V _B (0 to −3 V) between the emitter electrode and the base electrode. The amount of change (off current, on current) of I _B and collector current I _C was measured. Also, the ratio of the change in the base current to the change in the collector current, that is, the current amplification factor (h _FE ), and the on / off ratio (I _C-ON / I _C-OFF ) that is the ratio between the on-current and off-current are calculated did.

Example 1
[Collector layer: CuPc / DIP, emitter layer: pentacene]
An ITO transparent substrate is used as a collector electrode, and a p-type organic semiconductor layer having an average thickness of 240 nm made of copper phthalocyanine (CuPc), which is a p-type organic semiconductor material, is formed on the substrate as a collector electrode side collector layer. A base electrode side collector layer made of DIP and having an average thickness of 160 nm was formed on each by a vacuum deposition method, and a collector layer having a structure in which the two different layers were laminated was produced. The obtained collector layer surface had a roughness of RMS = 1.68 nm and an average crystal grain size of 26 nm. Next, a 3 nm current transmission facilitating layer made of lithium fluoride was formed on the collector layer, and a base electrode layer made of aluminum and having an average thickness of 10 nm was formed thereon by a vacuum deposition method. Then, the dark current suppression layer which consists of aluminum oxide was formed in the aluminum electrode surface by heat processing for 1 hour at 150 degreeC in air | atmosphere. Further, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and then a p-type organic semiconductor layer (average film thickness: 100 nm) made of pentacene was laminated as an emitter layer by a vacuum deposition method. Next, an emitter electrode 12 made of gold and having an average thickness of 30 nm was formed thereon by a film forming means using a vacuum deposition method, and the layers and the electrodes were laminated in the order described above to obtain the transistor element of Example 1.

The transistor characteristics of the transistor element of Example 1 obtained as described above are shown in Table 1. The output characteristics of the transistor element of Example 1 are as follows: a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. 0 to −3 V), and the change amount of the collector current I _C and the base current I _B was measured. 4 and 5 show changes in collector current (I _C -V _B characteristics) and base current when a base voltage is applied. Further, when the collector voltage V _C = −5 V and the base voltage V _B = −3 V are applied, the collector current I _C on-current, current amplification factor, off-current when V _B = 0 V, and on / off The ratio is shown in Table 1.

(Example 2)
[Collector layer: CuPc / DNTT, emitter layer: pentacene]
An ITO transparent substrate is used as a collector electrode, and a p-type organic semiconductor layer having an average thickness of 300 nm made of copper phthalocyanine (CuPc), which is a p-type organic semiconductor material, is formed on the substrate as a collector electrode side collector layer. A base electrode side collector layer having an average thickness of 100 nm made of DNTT was formed on each of the layers by a vacuum vapor deposition method, and a collector layer having a structure in which the two different layers were laminated was produced. The obtained collector layer surface had a roughness of RMS = 13.6 nm and an average crystal particle size of 107 nm. Next, a 3 nm current transmission facilitating layer made of lithium fluoride was formed on the collector layer, and a base electrode layer made of aluminum and having an average thickness of 10 nm was formed thereon by a vacuum deposition method. Then, the dark current suppression layer which consists of aluminum oxide was formed in the aluminum electrode surface by heat processing for 1 hour at 150 degreeC in air | atmosphere. Further, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and then a p-type organic semiconductor layer (average film thickness: 100 nm) made of pentacene was laminated as an emitter layer by a vacuum deposition method. Next, an emitter electrode 12 made of gold and having an average thickness of 30 nm was formed thereon by a film forming means using a vacuum vapor deposition method, and the layers and the electrodes were laminated in the order described above to obtain the transistor element of Example 2.

The transistor element of Example 2 obtained as described above exhibited current modulation which is a characteristic of MBOT. The output characteristics of the obtained transistor element are as follows: a collector voltage V _C of −10 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. ˜−4 V), the change amount of the collector current I _C and the base current I _B was measured. As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3 V are applied, the on-current density I _C-ON of the collector current I _C = 61.7 mA / cm ² and the current amplification factor h _FE = The off-current density I _C-OFF = 5.9 × 10 ⁻² mA / cm ² at 715.3 and V _B = 0V, and the on / off ratio was 1.1 × 10 ³ .

(Examples 3 to 8)
[Collector layer: CuPc / DIP, emitter layer: pentacene]
In the transistor element of Example 1, the total thickness of the collector layer having a two-layer structure is the same at 400 nm, and the thickness of the p-type organic semiconductor layer formed from each material of copper phthalocyanine and diindenoperylene is shown in Table 2. The transistor elements of Examples 3 to 8 were fabricated in the same manner as in Example 1 except that the collector layer was formed with the thickness changed as described above.

  Specifically, an ITO transparent substrate is used as a collector electrode, and a collector electrode side collector layer is formed on the substrate, and the average thickness of copper phthalocyanine (CuPc), which is a p-type organic semiconductor material, is 390, 350, 320, 300, 280, and 200 nm p-type organic semiconductor layers were formed by vacuum deposition. Furthermore, as a base electrode side collector layer laminated | stacked on it, the p-type organic-semiconductor layer whose average thickness which consists of DIP is respectively 10, 50, 80, 100, 120, 200 nm was produced by the vacuum evaporation method. . Next, a 3 nm current transmission promoting layer made of lithium fluoride was formed on each of the collector layers obtained above, and then a base electrode layer made of aluminum and having an average thickness of 10 nm was formed by vacuum deposition. . Then, the dark current suppression layer which consists of aluminum oxide was formed in the aluminum electrode surface by heat processing for 1 hour at 150 degreeC in air | atmosphere. Further, a 3 nm current transmission facilitating layer made of lithium fluoride was formed thereon, and then a p-type organic semiconductor layer (average film thickness 100 nm) made of pentacene was laminated as an emitter layer by a vacuum evaporation method. Next, an emitter electrode 12 made of gold and having an average thickness of 30 nm was formed by a film forming means by vacuum vapor deposition, and laminated in the order described above to obtain transistor elements of Examples 3 to 8. The structure of the obtained transistor element is shown in FIG. 2, and the characteristics are summarized in Table 2.

Example 9
[Collector layer: CuPc / NiPc, emitter layer: pentacene]
In the transistor element of Example 2, the base electrode side collector layer was changed from dinaphthothienothiophene (DNTT) to nickel phthalocyanine (NiPc), and other than that, the transistor element of Example 9 was obtained in the same manner as Example 2. It was. Specifically, an ITO transparent substrate is used as a collector electrode, and an organic semiconductor layer having an average thickness of 300 nm made of copper phthalocyanine (CuPc), which is a p-type organic semiconductor material, is formed on the substrate as a collector electrode side collector layer. Further, a base electrode side collector layer made of NiPc and having an average thickness of 100 nm was formed thereon by a vacuum deposition method. The obtained collector layer surface had a roughness of RMS = 8.36 nm and an average crystal particle diameter of 41 nm. Next, a 3 nm current transmission promoting layer made of lithium fluoride was formed on the collector layer, and a base electrode layer made of aluminum and having an average thickness of 10 nm was formed by vacuum deposition. Then, the dark current suppression layer which consists of aluminum oxide was formed in the aluminum electrode surface by heat processing for 1 hour at 150 degreeC in air | atmosphere. Further, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and then a p-type organic semiconductor layer (average film thickness: 100 nm) made of pentacene was laminated as an emitter layer by a vacuum deposition method. Next, an emitter electrode 12 made of gold and having an average thickness of 30 nm was formed thereon by a film forming means using a vacuum vapor deposition method, and was laminated in the order described above to obtain a transistor element of Example 9.

The obtained transistor element exhibited current modulation, which is a characteristic of MBOT. The output characteristics of the obtained transistor element are as follows: a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and a base voltage V _B is applied between the emitter electrode and the base electrode. -3V), the change amount of the collector current I _C and the base current I _B was measured. As a result, when the collector voltage V _C = −5 V and the base voltage V _B = −3 V are applied, the collector current I _C on-current density I _C-ON = 16.9 mA / cm ² , the current amplification factor h _FE = 25, off-current density I _C-OFF = 0.12 mA / cm ² when V _B = 0V, and the on / off ratio was 136.

(Comparative Example 1)
[Collector layer: CuPc, emitter layer: pentacene]
An ITO transparent substrate was used as a collector electrode, and a p-type organic semiconductor layer having an average thickness of 400 nm made of copper phthalocyanine (CuPc), which is a p-type organic semiconductor material, was formed on the substrate by a vacuum deposition method. Next, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and a base electrode layer made of aluminum and having an average thickness of 10 nm was formed thereon by a vacuum deposition method. Then, the dark current suppression layer which consists of aluminum oxide was formed in the aluminum electrode surface by heat processing for 1 hour at 150 degreeC in air | atmosphere. Further, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and then a p-type organic semiconductor layer (average film thickness: 100 nm) made of pentacene was laminated as an emitter layer by a vacuum deposition method. Next, an emitter electrode 12 made of gold and having an average thickness of 30 nm was formed thereon by a film forming means using a vacuum vapor deposition method and laminated in the order described above to obtain a transistor element of Comparative Example 1. The structure of the element is shown in FIG.

The transistor characteristics of the device of Comparative Example 1 obtained are shown in Table 1. The output characteristics of the transistor element obtained in Comparative Example 1 are not applied when the collector voltage V _C is applied by −10 V between the emitter electrode and the collector electrode and when the base voltage V _B is applied between the emitter electrode and the base electrode. (0 to -3V), the amount of change in the collector current I _C and the base current I _B was measured. 4 and 5 show changes in collector current (I _C -V _B characteristics) and base current when a base voltage is applied. Further, when the collector voltage V _C = −5 V and the base voltage V _B = −3 V are applied, the collector current I _C on-current, current amplification factor, off-current when V _B = 0 V, and on / off The ratio is shown in Table 1.

(Comparative Example 2)
[Collector layer: DIP, emitter layer: pentacene]
An ITO transparent substrate was used as a collector electrode, and an organic semiconductor layer having an average thickness of 400 nm made of diindenoperylene (DIP), which is a p-type organic semiconductor material, was formed on the substrate by a vacuum deposition method as a collector layer. Next, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and then a base electrode layer made of aluminum and having an average thickness of 10 nm was formed thereon by a vacuum deposition method. Then, the dark current suppression layer which consists of aluminum oxide was formed in the aluminum electrode surface by heat processing for 1 hour at 150 degreeC in air | atmosphere. Further, a 3 nm current transmission promoting layer made of lithium fluoride was formed thereon, and then a p-type organic semiconductor layer (average film thickness: 100 nm) made of pentacene was laminated as an emitter layer by a vacuum deposition method. Next, an emitter electrode 12 made of gold and having an average thickness of 30 nm was formed by a film forming means using a vacuum evaporation method, and laminated in the order described above to obtain a transistor element of Comparative Example 2.

The transistor characteristics of the obtained transistor element are shown in Table 1. The output characteristics of the transistor element obtained in Comparative Example 2 are not applied when the collector voltage V _C is applied by −10 V between the emitter electrode and the collector electrode and when the base voltage V _B is applied between the emitter electrode and the base electrode. (0 to -3V), the amount of change in the collector current I _C and the base current I _B was measured. 4 and 5 show changes in collector current (I _C -V _B characteristics) and changes in base current when a base voltage is applied. Further, when the collector voltage V _C = −5 V and the base voltage V _B = −3 V are applied, the collector current I _C on-current, current amplification factor, off-current when V _B = 0 V, and on / off The ratio is shown in Table 1.

(Evaluation results)
The output characteristics of the transistor element are that when a collector voltage V _C of -5 V is applied between the emitter electrode and the collector electrode, and when a base voltage V _B is applied between the emitter electrode and the base electrode, and when not applied (0 to -3 V). The amount of change in the collector current I _C and the base current I _B was measured. The transistor elements of the examples were confirmed to operate as MBOT.
From the comparison with the device of the comparative example, it was confirmed that the transistor device of the present invention has an excellent collector current value and on / off ratio when the collector layer has a laminated structure of two or more layers. In addition, it was confirmed that by making the p-type organic semiconductor layer of the collector layer laminated on the base electrode a smooth surface, further excellent performance was obtained and transistor characteristics expected to be put to practical use were obtained.

  Since the organic transistor element of the present invention has a small off-current and a high on / off ratio, it can be used as a display driving element such as an organic EL or an organic light-emitting transistor element incorporating an organic light-emitting layer. It is expected to be used in various fields.

10: Substrate 11: Collector electrode 12: Emitter electrode 13: Base electrode 21: Organic semiconductor layer (emitter layer)
22: Organic semiconductor layer (collector layer)
22A: Organic semiconductor layer (base electrode side collector layer)
22B: Organic semiconductor layer (collector electrode side collector layer)

Claims (10)

In a transistor element having a stacked structure in which a sheet-like base electrode is disposed between an emitter electrode and a collector electrode, and a p-type organic semiconductor layer is provided on each of the front and back sides of the base electrode,
An organic semiconductor layer including at least one p-type organic semiconductor is provided between the emitter electrode and the base electrode, and is formed of the same or different p-type semiconductor material between the base electrode and the collector electrode. A laminated structure in which two p-type organic semiconductor layers having different HOMO levels (maximum occupied orbital energy levels) are sequentially laminated (provided that an organic EL element portion is provided between the base electrode and the collector electrode). And a collector layer having a hole injection layer and a hole transport layer stacked in that order) , and a collector electrode side collector layer with respect to the HOMO level of the collector electrode side collector layer. A transistor element characterized in that a collector layer has a large HOMO level .   The laminated structure in which the two different p-type organic semiconductor layers are sequentially laminated is composed of two organic semiconductor layers, ie, a collector electrode side collector layer and a base electrode side collector layer, and the collector electrode side collector layer has a HOMO level (maximum (Occupied orbital energy level) consists of a p-type organic semiconductor layer at 4.5 to 5.5 eV, and the base electrode side collector layer has a HOMO level (maximum occupied orbital energy level) of 5.0 to 6.0 eV 2. The transistor element according to claim 1, wherein the HOMO level (maximum occupied orbital energy level) of the base electrode side collector layer is higher than that of the collector electrode side collector layer.   The roughness of the surface of each p-type organic semiconductor layer forming a laminated structure in which two p-type organic semiconductor layers having different collector layers are sequentially laminated is 5 nm or less in terms of mean square roughness (RMS). 3. The transistor element according to claim 1 or 2.   The organic semiconductor layer disposed on the base electrode side of the plurality of p-type organic semiconductor layers forming a stacked structure in which two p-type organic semiconductor layers having different collector layers are sequentially stacked is diindeno The transistor element according to claim 1, comprising perylene, dinaphthothienothiophene, phthalocyanine, and derivatives thereof.   Of the p-type organic semiconductor layers forming a stacked structure in which two p-type organic semiconductor layers having different collector layers are sequentially stacked, the organic semiconductor layer disposed on the collector electrode side is formed of phthalocyanine, diindeno The transistor element according to claim 1, comprising perylene and a derivative thereof.   6. The transistor element according to claim 1, wherein the p-type organic semiconductor layer disposed between the emitter electrode and the base electrode contains pentacene, phthalocyanine, and derivatives thereof.   7. The transistor element according to claim 1, further comprising a current transmission facilitating layer in a state of being laminated on one or both of the front and back surfaces of the sheet-like base electrode.   The transistor element according to claim 7, wherein the current transmission promoting layer is made of lithium fluoride.   The transistor element according to claim 7 or 8, wherein the current transmission promoting layer has a thickness of 0.1 nm to 100 nm. A collector current I _C-ON that flows by applying a voltage (V _B ) between the emitter electrode and the base electrode, and further applying a voltage (V _C ) between the emitter electrode and the collector electrode; ON / OFF, which is the ratio of the collector current I _C-OFF that flows when the voltage (V _C ) is applied between the emitter electrode and the collector electrode without applying the voltage (V _B ) between the base electrode and the base electrode The transistor element according to any one of claims 1 to 9, wherein the transistor element exhibits a current modulation property such that (I _C-ON / I _C-OFF ) is 1,000 or more.

Images